New Methods for Stereoselective Synthesis of α-Alkylidene-γ-butyrolactones Using Monoanion of<i>O</i>-Ethyl<i>S</i>-(Tetrahydro-2-oxo-3-furanyl) Thiocarbonate and Dianion of α-Mercapto-γ-butyrolactone
The lithium enolates of O-ethyl S-(tetrahydro-2-oxo-3-furanyl) dithiocarbonate and thiocarbonate were found to be efficient reagents for the stereoselective synthesis of α-alkylidene-γ-butyrolactones fromcarbonylcompounds. The dianion of α-mercapto-γ-butyrolactone was successfully generated by treatment of α-mercapto-γ-butyrolactone with 2.2 equivalents of lithium diisopropylamide in the presence